Orontes, Arab. Nahr al-Asi, river, c.250 mi (400 km) long, rising in the northern part of the Al Biqa valley, Lebanon, and flowing generally N through Syria, then W into S Turkey and into the Mediterranean Sea; celebrated because of the antiquity of settlement along its banks. The river is unnavigable but is important for irrigation, especially in Syria. Marshes on its middle course have been drained and the land reclaimed for farming. On its lower course, the river has cut below the surrounding plain, and it is noted for remarkable water wheels, from 20 to 70 ft (6-21 m) in diameter, at Homs and Hama; the wheels, turned by the current, lift water onto the plains.